[whatwg] Clarify how to indicate document hierarchy

[James Graham]

Spartanicus wrote:
> IMO a spec should primarily describe the building blocks, i.e. the
> available elements and if needed illustrate their usage with minimal
> context. How to use those elements to build a page or site is up to
> authors. It depends on variables such UA features and support, UA market
> share, user behaviour, fashions, fads and other slippery modalities.
> This IMO is not something a spec should get involved with.

Whilst the spec should never mandate app UI, it certainly should provide 
enough guidance that the usage of elements between pages is consistent; 
otherwise it is somewhere between very difficult and impossible to make 
UA features that make use of the semantics features that the language is 
supposed to provide due to the variation in usage between pages.

As for headings, if you want to get a feel for how headings are used on 
the web, may I humbly suggest my Firefox extension[1] for displaying the 
  headings in a sidebar. It has a "liberal" (i.e. useful) interpretation 
of the HTML4 spec in that a <h6> following a <h1> will be shown as a 
direct child of the <h1>.

[1] https://addons.mozilla.org/firefox/475/

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